1. Field of the Invention
The present invention relates to a solder joint determination method for inspecting and determining a solder joint condition of an electrode of an electronic part mounted on a circuit board by soldering, a solder inspection method, and a solder inspection device.
2. Description of the Related Art
In the related art, generally, an electrode of an electronic part, which is mounted on a circuit board, is attached to the circuit board by soldering, and in the inspecting step subsequent to the soldering step, it is determined whether the solder and the electrode are joined reliably. In this inspecting step, it is also determined whether there are defective soldering conditions, such as absence of the solder, and lack of wetting.
For example, a solder inspection device irradiates a light beam, such as a laser beam, onto an inspection site, performs optical scanning, measures optical changes of a reflected light beam from the inspection site, and then performs data analysis. From the results, the solder inspection device determines shapes of the inspection sites, locations of the inspection sites, and additionally, calculates lengths and heights of the solder at the soldering sites, and determines positions of parts and lack of wetting.
For example, Japanese Patent Gazette No. 3055161 (hereinafter referred to as “reference 1”), and Japanese Laid-Open Patent Application No. 5-332745 (hereinafter referred to as “reference 2”) disclose such a technique.
In these years, as a response of manufacturers to the environmental problems, in the mounting technology, solder free from lead, which is known as “lead-free solder”, is more and more used. However, the lead-free solder suffers from a problem in the wetting property compared to the common lead-included solder. For example, Japanese Laid-Open Patent Application No. 2003-101216 (hereinafter referred to as “reference 3”) disclose related issues.
FIG. 11 is a schematic view of a solder inspecting device and an inspection site for illustrating a solder inspecting method in the related art.
In FIG. 11, there are a circuit board 1, an electronic part 2 mounted on the circuit board 1, soldered portions 3 which join electrodes 2a of the electronic part 2 with the circuit board 1, a laser 4 which emits a laser beam Lo used for soldering inspection, a deflecting mirror 5 which deflects the laser beam Lo to pass across the soldered portions 3 for scanning, and light receiving elements 6 which receive light beams Lr reflected from the electrodes 2a. 
In FIG. 11, the deflecting mirror 5 is driven to deflect the laser beam Lo to pass across the soldered portions 3 in an X direction as shown in FIG. 11, and move the laser beam Lo in a Y direction as shown in FIG. 11, so that the light beams Lr reflected from the electrodes 2a are received by the light receiving elements 6. In the light receiving elements 6, electro-optical conversion is carried out, and the shape of the soldered portions 3 is detected and measured through data processing and image processing; then the measured results are compared with preset conditions to determine soldering conditions.
FIG. 12A through FIG. 12C are front views (upper portion) and plan views (lower portion) of soldered portions for illustrating determination results by the solder inspecting method as shown in FIG. 11.
In the solder inspecting method of the related art, the laser beam Lo is scanned to pass across two sites (indicated by circles) of the soldered portions 3. As shown in FIG. 12A, there is a portion (indicated by “A”) having an inclined surface at the end of the soldered portion 3, and a flat portion (indicated by “B”) near the center portion of the soldered portion 3. It is determined that the soldering condition is good if the soldered portion 3 has such a shape.
Therefore, if the soldering condition is like that in FIG. 12A, it can be determined that the soldering condition is good by visual inspection and by an inspection with a soldering inspection device of the related art.
If the soldering condition is like that in FIG. 12C, it can be determined that the soldering condition is not good by visual inspection and by the inspection with the soldering inspection device of the related art.
However, if the soldering condition is like that in FIG. 12B, since the soldered portion 3 is connected with the electrode 2a, it is determined that the soldering condition is good by visual inspection, but it is determined that the soldering condition is not good by the inspection with the soldering inspection device of the related art, since the soldering condition in FIG. 12B is not in agreement with the preset good soldering conditions.
That is, in the related art, the soldering inspection device suffers from problems in precision and accuracy compared to visual inspection.
Additionally, when the lead-free solder is used for soldering, as described above, the lead-free solder suffers from the problem in that the wetting property is degraded compared to the common lead-included solder. Due to this, it is desirable that inspection of the joint portion between the electrodes 2a and the soldered portions 3 by using an inspection device and determination of good soldering condition be made with high precision.